This invention relates to a small size, portable bender for bending a steel rod or tube, and particularly to a bending machine capable of being transported and easily placed on the spot by the hands of a user himself without involving any other expedients, and operated by an AC electric source of the domestic order of 100 volts.
Such a small size, portable bending machine is disclosed in my U.S. Pat. application No. 712,144, now U.S. Pat. No. 4,052,875. The disclosed bending machine includes a drive shaft adapted to be turned by a drive force against action of return spring means for actuation of a bending member, a clutch interposed to transmit the drive force to the drive shaft, and bending angle control means responsive to an adjusted angular position of the drive shaft for disconnecting the clutch when the drive shaft and being member have turned to the adjusted angular position. A steel rod or tube can be thus bent to an intended angle. After the bending operation, the return spring means act to urge the drive shaft and the related bending means toward the home position, building up kinetic moment to a fairly great degree until the drive shaft and its related components including the bending member, reach the home position where the accumulated moment is then annihilated to cause a substantial impact. This obviously generates somewhat offensive noises and causes wear and tear in the moving machine components.
When the machine operates to bend a certain number of steel rods or tubes one after another to a predetermined angle, as ordinarily is the case, such impact generated after each cycle of the bending operation will place the machine in vibratory conditions that a mechanical arrangement incorporated for a user to manually preset an intended bending angle is likely to be shifted from a position which has been preset for the intended bending angle. If the angle preset arrangement is so shifted to a different position, steel rods or tubes can no more be bent to the initially preset bending angle so that the cyclic bending operation has to be interrupted for corrective resetting of the intended bending angle.
The bending machine under discussion, moreover, often proves unsatisfactory in preciseness of selected degrees of angle to which materials are desired to be bent because the angle preset arrangement cannot provide a substantially continuous selection but only a stepwise selection of bending angles, because of its structural limitations.